Thermomechanical machines, which are exposed to high temperatures, are used in steam power plants and in gas and steam turbine power plants in the field of local power supply. Steam turbines have various turbine components and are generally designed with a large volume. During operation, the aforementioned turbine components are exposed both to erosive and corrosive wear and also to mechanical wear. This constant loading of the turbine components leads to instances of material disintegration and/or to material losses. This considerably reduces the service life of the turbine components, which also has an effect on the operational reliability of the steam turbine plant as a whole. The corrosive or erosive phenomena on the turbine components are, for example, erosion corrosion, drop impingement erosion, sliding wear, rolling wear, corrosion and oxidation.
Various measures are taken in order to protect the turbine components against the aforementioned wear mechanisms. For instance, these turbine components are often provided with layers having an increased wear resistance and/or corrosion resistance compared to the base material of the turbine component. Various processes are known for applying protective layers to a base material. The following are known, inter alia: thermal spraying, brazing, CVD, PVD, electrodeposition and build-up welding.
However, on account of the properties of the turbine components, not every one of the aforementioned processes is suitable for applying a protective layer to a turbine component. By way of example, thermal spraying may not be possible on account of a complicated turbine component geometry. Furthermore, a furnace process might be excluded as a result of the in some cases very large geometries of the structural parts. Further processes may be excluded if the intention is to coat only certain locations of the turbine component rather than the entire turbine component for reasons of fatigue strength or costs. It is often the case that the aforementioned processes require space, which in some situations, e.g. during overhaul, is not present. Therefore, various processes are also excluded on account of a lack of required space. Finally, it might be the case that the aforementioned processes cannot be used if the process itself unfavorably influences the base material or gives rise to distortion, e.g. by the introduction of heat during brazing in a furnace. Therefore, it is generally the case that the turbine components are provided with a protective layer in such a manner that individual solutions are developed, leading to an optimum solution, i.e. to a suitable layer. Solutions of this nature are, however, sometimes very costly, e.g. if it is necessary to operate with maskings or if process parameters, e.g. the brazing temperature, have to be limited so as not to influence the turbine component through a change in the base material or distortion which occurs.